Zaru Go (ザル碁) is a rule set propounded by Iehiro? at http://www.vimage.co.jp/~iehiro/cgi-bin/gocaffe/sub4_2.htm.
When a player passes he gives the opponent one stone as a captive.
The game ends with two consecutive passes.
Each player's score is the number of captives he has.
Other rules are as in regular go.
Bill: Iehiro develops zarugo step by step, starting from atari go, which he calls pon go. He points out that Zaru Go is equivalent to stone counting if White must make the last pass, à la AGA rules.
See also Zaru Go Problem 1